This invention relates to a multi-axial manipulator for a medical instrument or the like, such as a laser knife, an optical coagulator, a laser machining device, etc.
Carbonic acid gas lasers and argon lasers have recently been employed as medical instruments, and in such use a manipulator is necessary to enable the doctor or user to easily guide the laser beam onto the object to be operated on. In general, such a manipulator comprises a tube or tubes for guiding the laser beam, mirrors for appropriately reflecting the beam, and a condenser lens. In order to move the focused light spot to a desired position in a given cubical space, it is typically necessary to arrange one or more mirrors at each hinge joint of the manipulator, and to rotate each mirror around the in-coming or out-going light axis in order to maintain proper optical alignment. As the conventional manipulator has a large number of pivot arms and reflecting mirrors, its optical path is necessarily quite long and the accurate alignment thereof requires a very precise, complicated, and costly mechanism.
The overall manipulator arrangement or mechanism is similar to that of a belt driven dental drill, where the power or drive source is stationary and the relatively small hand held chuck member is coupled to the source through a plurality of pivot arms. Here, the drive source is the laser generator, and mirrors must be provided at each hinge or pivot joint to keep the laser beam accurately centered within the hollow pivot arms as the user (surgeon) freely manipulates a hand held outward wand or pencil probe.
Recently, a small and powerful carbonic acid gas laser has been developed, whereby the laser generating apparatus has become more portable than before. Thus, if the laser generator is mounted on a portable operating stand whereby its position can be coarsely controlled horizontally and vertically, and if the angle of elevation of the output beam can also be coarsely controlled, it is possible to generally bring the beam to the vicinity of a patient or object to be operated on. A conventional long arm manipulator is unnecessary and unsuitable for such an application, which requires a short arm mechanism which can finely and accurately control the position of the focused laser beam onto a target spot. In addition, a high degree of user and output probe freedom is required of the manipulator, which is not provided by the conventional mechanism.
An example of a conventional or prior art manipulator is schematically shown in FIG. 1, wherein a laser beam S is reflected at the centers a.sub.1, a.sub.2, a.sub.3, a.sub.4 and a.sub.5 of the mirrors 1, 2, 3, 4 and 5, respectively, and forms a small light spot (about 0.1 mm in diameter) at a focal point T through a condenser lens 30. The X, Y and Z coordinates are oriented as shown in the figure, and the small white circles on the optical axes designate the mirror rotation axes. That is, mirrors 1, 3, 4 and 5 can rotate around the axes X.sub.1, Y.sub.1, X.sub.2 and Y.sub.2, respectively. Accordingly, the light spot T can be accurately moved to a desired coordinate in the horizontal plane X.sub.3 Y.sub.3, which is assumed to represent an object or subject to be operated on, or to a desired coordinate in a given vertical plane such as X.sub.3 Z.sub.3 and Y.sub.3 Z.sub.3. A fine control mechanism (not shown) accurately adjusts the reflecting mirrors to form 45.degree. angles with the respective incident light beams and directs the rotation centers of the incident light spots onto the mirror surfaces. It is important that the laser light can be applied, at a desired angle of incidence, to the target surface plane X.sub.3 Y.sub.3. In most operations the laser light is applied vertically to the object to be operated on. For this reason, the mirror rotations on each of the X- and Y-axes are opposite to each other, that is, the rotation of the mirrors on the X.sub.1 - and X.sub.2 - (Y.sub.1 - and Y.sub.2 -) axes are opposite to each other.
FIG. 3 shows a conventional mirror rotation mechanism, wherein a laser light beam 6 is perpendicularly reflected by the surface 7 of a mirror 10 to an out-going light beam 8. A bearing 12 is mounted in a mirror holder 9 so that an inlet tube 11 can rotate around an optical axis 6-7. No matter how the mirror holder 9 rotates, it is necessary that the outgoing light beam 8 lie on the center axis of the outlet tube 13, and for this purpose a fine control mechanism (not shown) is required to set the mirror 10 at precisely 45.degree. and to properly position the reflecting point on the mirror surface.